Gallium oxide diode

Abstract

To provide a gallium oxide diode including Ga2O3 in a semiconductor layer and having a structure that can avoid the decrease in reliability due to oxidation of an electrode.SOLUTION: A gallium oxide diode 1 includes an n-type Ga2O3 layer 10, an n-type oxide semiconductor layer 11 stacked on the Ga2O3 layer 10, an anode electrode 12 forming ohmic junction with the oxide semiconductor layer 11, and a cathode electrode 13 forming ohmic junction with the Ga2O3 layer 10. The electron affinity of the oxide semiconductor layer 11 is larger than the electron affinity of a part of the Ga2O3 layer 10 that is in contact with the oxide semiconductor layer 11, and the rectification is secured by the offset of a bottom edge of a conduction band in the junction part between the Ga2O3 layer 10 and the oxide semiconductor layer 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gallium oxide diode. [Background technology]

[0002] Conventionally, a Schottky barrier diode using Ga2O3 in a semiconductor layer is known (for example, Patent Document 1). In the Schottky barrier diode described in Patent Document 1, an anode electrode is connected to the Ga2O3 layer to form a Schottky junction, thereby ensuring rectification. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-102081 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the Schottky barrier diode described in Patent Document 1, the anode electrode connected to the Ga2O3 layer is oxidized by oxygen contained in the Ga2O3 layer, and the height of the potential barrier at the interface between the Ga2O3 layer and the anode electrode changes, which changes the conduction loss and breakdown voltage of the diode. The change in conduction loss and breakdown voltage may cause a decrease in the reliability of the diode.

[0005] An object of the present invention is to provide a gallium oxide diode using Ga2O3 for a semiconductor layer, which has a structure capable of preventing a decrease in reliability due to oxidation of the electrodes. [Means for solving the problem]

[0006] In order to achieve the above object, one aspect of the present invention provides the following [1] to [ 7 ] gallium oxide diodes are provided.

[0007] [1] A semiconductor device comprising: an n-type Ga2O3 layer; an n-type oxide semiconductor layer laminated on the Ga2O3 layer; an anode electrode forming an ohmic junction with the oxide semiconductor layer; and a cathode electrode forming an ohmic junction with the Ga2O3 layer; The oxide semiconductor layer has a thickness of 1×10 18 cm -3 having a donor concentration of a gallium oxide diode in which the electron affinity of the oxide semiconductor layer is greater than the electron affinity of a portion of the Ga2O3 layer that is in contact with the oxide semiconductor layer, and rectification is ensured by an offset of the conduction band bottom at a junction between the Ga2O3 layer and the oxide semiconductor layer. [2] The gallium oxide diode according to [1] above, wherein a difference between an electron affinity of the Ga2O3 layer and an electron affinity of a portion of the oxide semiconductor layer in contact with the Ga2O3 layer is 0.4 eV or more. [3] The gallium oxide diode according to [1] or [2] above, wherein the oxide semiconductor layer is made of an oxide semiconductor containing at least one of ZnO, TiO2, In2O3, and SnO2. [4] The gallium oxide diode according to any one of the above [1] to [3], wherein the oxide semiconductor layer is made of a plurality of oxide semiconductors having different electron affinities. [ 5 ] The oxide semiconductor layer has a thickness of 10 nm or more, 4 13. A gallium oxide diode according to claim 12. [ 6 ] Any of the above [1] to

[10] , wherein the Ga2O3 layer has a trench on the surface on the anode electrode side, the inner surface of the trench is covered with a trench insulating film, a part of the anode electrode is embedded inside the trench insulating film in the trench, and at least a part of the oxide semiconductor layer is formed between a mesa-shaped portion between adjacent trenches of the Ga2O3 layer and the anode electrode. 5 13. A gallium oxide diode according to claim 12. [ 7] Any of the above [1] to

[10] , wherein the Ga2O3 layer has a trench on the surface facing the anode electrode, the inner surface of the trench is covered with a p-type semiconductor material, and at least a part of the oxide semiconductor layer is formed between a mesa-shaped portion between adjacent trenches of the Ga2O3 layer and the anode electrode. 5 13. A gallium oxide diode according to claim 12. Effect of the Invention

[0008] According to the present invention, it is possible to provide a gallium oxide diode using Ga2O3 for a semiconductor layer, which has a structure capable of preventing a decrease in reliability due to oxidation of the electrodes. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a vertical sectional view of a gallium oxide diode according to a first embodiment of the present invention. [Diagram 2] FIG. 2 shows the band diagrams of Ga2O3, which is the material of the Ga2O3 layer, various oxide semiconductors which are examples of candidate materials for the oxide semiconductor layer, and the Fermi levels of various metals which are examples of candidate materials for the anode electrode. [Diagram 3] FIG. 3 is a vertical sectional view of a gallium oxide diode according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a vertical sectional view of a gallium oxide diode according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] First Embodiment (Structure of gallium oxide diode) 1 is a vertical cross-sectional view of a gallium oxide diode 1 according to a first embodiment of the present invention. The gallium oxide diode 1 is a vertical diode including an n-type Ga2O3 layer 10, an n-type oxide semiconductor layer 11 stacked on the Ga2O3 layer 10, an anode electrode 12 connected to the oxide semiconductor layer 11, and a cathode electrode 13 connected to the Ga2O3 layer 10.

[0011] The electron affinity of the oxide semiconductor layer 11 is larger than that of the portion of the Ga2O3 layer 10 in contact with the oxide semiconductor layer 11, and rectification is ensured by the offset of the conduction band minimum at the junction between the Ga2O3 layer 10 and the oxide semiconductor layer 11. The magnitude of the offset of the conduction band minimum at the junction between the Ga2O3 layer 10 and the oxide semiconductor layer 11 is equal to the difference between the electron affinity of the oxide semiconductor layer 11 and the electron affinity of the portion of the Ga2O3 layer 10 in contact with the oxide semiconductor layer 11.

[0012] In the gallium oxide diode 1, by applying a forward voltage (positive potential on the anode electrode 12 side) between the anode electrode 12 and the cathode electrode 13, the potential barrier at the interface between the Ga2O3 layer 10 and the oxide semiconductor layer 11 as viewed from the Ga2O3 layer 10 is lowered, and a current flows from the anode electrode 12 to the cathode electrode 13. On the other hand, when a reverse voltage (negative potential on the anode electrode 12 side) is applied between the anode electrode 12 and the cathode electrode 13, no current flows due to the potential barrier at the interface between the Ga2O3 layer 10 and the oxide semiconductor layer 11.

[0013] The Ga2O3 layer 10 is a layer made of Ga2O3 containing donors such as Sn and Si, and is typically made of a substrate 101 made of Ga2O3 and an epitaxial film 102 made of Ga2O3 formed thereon, as shown in Fig. 1. In this case, the epitaxial film 102 is the portion of the Ga2O3 layer 10 that contacts the oxide semiconductor layer 11. A buffer layer may be formed between the substrate 101 and the epitaxial film 102.

[0014] The substrate 101 is a substrate made of a single crystal of Ga2O3 having a β-type crystal structure. The substrate 101 contains donors such as Si and Sn. The donor concentration of the substrate 101 is, for example, 1.0×10 18 cm -3 That's it, 1.0 x 10 20 cm -3 The thickness of the substrate 101 is, for example, in the range of 10 μm to 600 μm.

[0015] The epitaxial film 102 is a film made of a single crystal of Ga2O3 having a β-type crystal structure. The epitaxial film 102 contains donor impurities such as Si and Sn. The donor concentration of the epitaxial film 102 is, for example, 1×10 13 cm -3 That's it, 1×10 18 cm -3 The thickness of the epitaxial film 102 is, for example, in the range of 1 μm or more and 100 μm or less.

[0016] As described above, the electron affinity of the oxide semiconductor layer 11 is greater than the electron affinity of the Ga2O3 layer 10 at a portion in contact with the oxide semiconductor layer 11. For example, when the Ga2O3 layer 10 is composed of the substrate 101 and the epitaxial film 102, the electron affinity of the oxide semiconductor layer 11 is greater than the electron affinity of the epitaxial film 102.

[0017] Furthermore, if the difference (Δχ) between the electron affinity of the oxide semiconductor layer 11 and the electron affinity of the Ga2O3 layer 10 at a portion in contact with the oxide semiconductor layer 11 is small, the turn-on voltage of the gallium oxide diode 1 decreases, while the reverse breakdown voltage decreases. To ensure a certain level of reverse breakdown voltage (e.g., 400 V or more), Δχ is preferably 0.4 eV or more, and more preferably 0.6 eV or more.

[0018] 2 shows band diagrams of Ga2O3, which is the material of the Ga2O3 layer 10, various oxide semiconductors which are candidate materials for the oxide semiconductor layer 11, and the Fermi levels of various metals which are candidate materials for the anode electrode 12. The numbers in the band diagram indicate the size of the band gap [eV], the numbers above the band diagram indicate the difference in electron affinity between the oxide semiconductor and Ga2O3 (the energy difference at the bottom of the conduction band) [eV], and the numbers above the Fermi levels indicate the difference in electron affinity between the metal and Ga2O3 (the energy difference between the bottom of the conduction band of Ga2O3 and the Fermi level of the metal) [eV].

[0019] According to FIG. 2, by using ZnO, TiO2, In2O3, or SnO2 as the material for the oxide semiconductor layer 11, Δχ can be made equal to or greater than 0.4 eV.

[0020] The oxide semiconductor layer 11 may be made of a plurality of oxide semiconductors having different electron affinities. By mixing oxide semiconductors having different electron affinities, the electron affinity of the oxide semiconductor layer 11 can be adjusted, and the turn-on voltage of the gallium oxide diode 1 can be controlled. For example, by mixing ZnO with about 17% or more of In2O3, Δχ can be made 0.6 eV or more. When the oxide semiconductor layer 11 is formed by sputtering, the oxide semiconductor layer 11 in which In2O3 and SnO2 are mixed can be formed inexpensively by using an indium tin oxide (ITO) target.

[0021] In order to adjust the turn-on voltage of the gallium oxide diode 1, an oxide having a larger electron affinity than the Ga2O3 layer 10, such as ZnO, TiO2, In2O3, or SnO2, may be used as a base, and an oxide having a smaller electron affinity than the Ga2O3 layer 10, such as Li2O, MgO, Al2O3, SiO2, NiO, CuO, or CuO2, may be mixed. However, the mixture ratio must be adjusted so that the electron affinity of the oxide semiconductor layer 11 made of the mixture is larger than that of the Ga2O3 layer 10.

[0022] In order to reduce the forward loss of the gallium oxide diode 1, the oxide semiconductor layer 11 preferably has a sufficiently high donor concentration. For example, 18 cm -3 The donor concentration of the oxide semiconductor layer 11 does not have any particular upper limit, and the upper limit of the doping concentration of each material is the upper limit of the donor concentration of the oxide semiconductor layer 11.

[0023] In order to ensure sufficient rectification of the gallium oxide diode 1, it is preferable that the oxide semiconductor layer 11 has a certain thickness, for example, a thickness of 10 nm or more, so that the anode electrode 12 does not affect the energy state (offset of the bottom of the conduction band) of the junction between the Ga2O3 layer 10 and the oxide semiconductor layer 11. In order to reduce forward loss, it is preferable that the thickness of the oxide semiconductor layer 11 is as thin as possible, for example, 200 nm or less.

[0024] The oxide semiconductor layer 11 may be amorphous, polycrystalline, single crystal, or the like. In general, when the growth temperature of the oxide semiconductor layer 11 is low, an amorphous oxide semiconductor layer 11 is obtained, and when the growth temperature is high, a polycrystalline oxide semiconductor layer 11 is obtained. When the conditions such as the crystal structure and growth conditions of the oxide semiconductor layer 11 and the orientation of the Ga2O3 layer 10 serving as the base for epitaxial growth are met, a single crystal oxide semiconductor layer 11 is obtained. In terms of manufacturing costs, the amorphous oxide semiconductor layer 11, which can be formed at a low temperature, is superior.

[0025] The method for forming the oxide semiconductor layer 11 is not particularly limited, and for example, high-frequency sputtering is superior in terms of manufacturing costs. Therefore, it is particularly preferable to form the amorphous oxide semiconductor layer 11 by using high-frequency sputtering in terms of manufacturing costs.

[0026] Although the oxide semiconductor layer 11 is in contact with the Ga2O3 layer 10, since the oxide semiconductor layer 11 is an oxide, there is no risk of the reliability of the gallium oxide diode 1 being reduced due to oxidation caused by oxygen contained in the Ga2O3 layer 10.

[0027] The anode electrode 12 is formed on the surface of the oxide semiconductor layer 11 opposite to the Ga2O3 layer 10, and forms an ohmic junction with the oxide semiconductor layer 11. As the material of the anode electrode 12, a material that forms an ohmic junction with the oxide semiconductor layer 11, that is, a material that has a work function close to or smaller than the electron affinity of the oxide semiconductor layer 11, can be used.

[0028] 2, the work functions of Pt, Ni, Au, Ti, and Al are close to or smaller than the energy (electric affinity) from the vacuum level to the bottom of the conduction band of TiO2, In2O3, and SnO2. Therefore, when the oxide semiconductor layer 11 is made of TiO2, In2O3, or SnO2, Pt, Ni, Au, Ti, or Al can be used as the material of the anode electrode 12.

[0029] In addition, since the work functions of Mo, Cu, and Fe are close to or smaller than the electron affinities of TiO2, In2O3, and SnO2, when the oxide semiconductor layer 11 is made of TiO2, In2O3, or SnO2, Mo, Cu, and Fe can also be used as materials for the anode electrode 12.

[0030] 2, the work functions of Ti and Al are close to or smaller than the energy (electric affinity) from the vacuum level to the bottom of the conduction band of ZnO. Therefore, when the oxide semiconductor layer 11 is made of ZnO, Ti or Al can be used as the material of the anode electrode 12.

[0031] Furthermore, since the work functions of Mo, Cu, and Fe are close to or smaller than the electron affinity of ZnO, when the oxide semiconductor layer 11 is made of ZnO, Mo, Cu, and Fe can also be used as materials for the anode electrode 12.

[0032] The anode electrode 12 may have a multi-layer structure. In this case, the layer in contact with the oxide semiconductor layer 11 is made of a material that forms an ohmic junction with the oxide semiconductor layer 11, such as Ti or Al.

[0033] Although the anode electrode 12 is in contact with the oxide semiconductor layer 11, even if the anode electrode 12 is oxidized by oxygen contained in the oxide semiconductor layer 11, there is almost no effect on the ohmic junction between the anode electrode 12 and the oxide semiconductor layer 11, and therefore there is almost no effect on the reliability of the gallium oxide diode 1.

[0034] The cathode electrode 13 is formed on the surface of the Ga2O3 layer 10 opposite to the oxide semiconductor layer 11, and forms an ohmic junction with the Ga2O3 layer 10. The cathode electrode 13 can be made of a material that forms an ohmic junction with the Ga2O3 layer 10, such as Ti or Al.

[0035] The cathode electrode 13 may have a multi-layer structure. In this case, the layer in contact with the Ga2O3 layer 10 is made of a material that forms an ohmic junction with the Ga2O3 layer 10, such as Ti or Al.

[0036] Although the cathode electrode 13 is in contact with the Ga2O3 layer 10, even if the cathode electrode 13 is oxidized by the oxygen contained in the Ga2O3 layer 10, there is almost no effect on the ohmic junction between the cathode electrode 13 and the Ga2O3 layer 10, and therefore there is almost no effect on the reliability of the gallium oxide diode 1.

[0037] The thickness of the anode electrode 12 is, for example, in the range of 0.03 μm to 5 μm, and the thickness of the cathode electrode 13 is, for example, in the range of 0.03 μm to 5 μm.

[0038] Second Embodiment The second embodiment of the present invention is different from the first embodiment in that the gallium oxide diode has a trench MOS structure. Note that the description of the same points as in the first embodiment will be omitted or simplified.

[0039] (Structure of gallium oxide diode) 3 is a vertical cross-sectional view of a gallium oxide diode 2 according to a second embodiment of the present invention. The gallium oxide diode 2 is a vertical Schottky diode having a trench MOS structure.

[0040] The gallium oxide diode 2 includes a substrate 201, an epitaxial layer 202 which is a layer formed on the substrate 201 and has a trench 203 opening on a surface 204 opposite the substrate 201 (the anode electrode 22 side), a trench insulating film 24 which covers the inner surface of the trench 203, an anode electrode 221 which is embedded inside the trench insulating film 24 in the trench 203, an anode electrode 222 which is formed on the surface 204 side of the epitaxial layer 202 and is electrically connected to the anode electrode 221, an oxide semiconductor layer 21 which is formed between the anode electrode 222 and a mesa-shaped portion 205 between adjacent trenches 203 of the epitaxial layer 202, and an oxide semiconductor layer 21 which is formed on the surface of the substrate 201 opposite the epitaxial layer 202.

[0041] The substrate 201 and the epitaxial layer 202 correspond to the substrate 101 and the epitaxial film 102 in the first embodiment, respectively, and constitute the Ga2O3 layer 20 corresponding to the Ga2O3 layer 10 in the first embodiment. The materials of the substrate 201 and the epitaxial layer 202 may be the same as those of the substrate 101 and the epitaxial film 102, respectively.

[0042] The oxide semiconductor layer 21 corresponds to the oxide semiconductor layer 11 according to the first embodiment. The material of the oxide semiconductor layer 21 may be the same as the material of the oxide semiconductor layer 11. The oxide semiconductor layer 21 has the same thickness as the oxide semiconductor layer 11. The oxide semiconductor layer 21 may be a single continuous film formed so as to cover the surface of the trench insulating film 24 in the trench 203, as shown in FIG. 3.

[0043] The anode electrode 22 constituted by the anode electrode 221 and the anode electrode 222 corresponds to the anode electrode 12 according to the first embodiment. The material of the anode electrode 22 may be the same as the material of the anode electrode 12.

[0044] The trench insulating film 24 is made of, for example, a single layer film of HfO2, Al2O3, SiO2, etc., or a laminated film of these. In particular, in order to suppress the electric field strength in the trench insulating film 24, it is preferable that the trench insulating film 24 contains HfO2, which has a high dielectric constant.

[0045] That is, in the gallium oxide diode 2, the Ga2O3 layer 20 has a trench 203 on a surface 204 facing the anode electrode 22, the inner surface of the trench 203 is covered with a trench insulating film 24, a part of the anode electrode 22 is embedded inside the trench insulating film 24 in the trench 203, and at least a part of the oxide semiconductor layer 21 is formed between the anode electrode 22 and a mesa-shaped portion 205 between adjacent trenches 24 of the Ga2O3 layer 20.

[0046] The electron affinity of the oxide semiconductor layer 21 is larger than the electron affinity of the epitaxial layer 202, which is the portion of the Ga2O3 layer 20 that is in contact with the oxide semiconductor layer 21, and rectification is ensured by the offset of the conduction band minimum at the junction between the mesa-shaped portion 205 of the Ga2O3 layer 20 and the oxide semiconductor layer 21.

[0047] The difference Δχ between the electron affinity of the oxide semiconductor layer 21 and the electron affinity of the portion of the Ga2O3 layer 20 in contact with the oxide semiconductor layer 21 is preferably 0.4 eV or more, and more preferably 0.6 eV or more, similar to the difference Δχ between the electron affinity of the oxide semiconductor layer 11 and the electron affinity of the Ga2O3 layer 10 in contact with the oxide semiconductor layer 11.

[0048] The oxide semiconductor layer 21 is in contact with the mesa-shaped portion 205 of the Ga2O3 layer 20, but since it is an oxide, there is no risk of the reliability of the gallium oxide diode 2 being reduced by oxidation caused by oxygen contained in the Ga2O3 layer 20. The anode electrode 22 is in contact with the oxide semiconductor layer 21, but even if the anode electrode 22 is oxidized by oxygen contained in the oxide semiconductor layer 21, there is almost no effect on the ohmic junction between the anode electrode 22 and the oxide semiconductor layer 21, so there is almost no effect on the reliability of the gallium oxide diode 2. The cathode electrode 23 is in contact with the Ga2O3 layer 20, but even if the cathode electrode 23 is oxidized by oxygen contained in the Ga2O3 layer 20, there is almost no effect on the ohmic junction between the cathode electrode 23 and the Ga2O3 layer 20, so there is almost no effect on the reliability of the gallium oxide diode 2.

[0049] In addition, the gallium oxide diode 2 may have a field plate structure as shown in FIG. 3 in order to suppress dielectric breakdown at the electrode end and further improve the breakdown voltage. That is, an insulating film 25 may be provided around the anode electrode 22 on the surface 204 of the epitaxial layer 202, and the edge of the anode electrode 22 may ride on the insulating film 25. The material of the insulating film 25 may be the same as the material of the trench insulating film 24. In addition, instead of the field plate structure, a guard ring structure made of a p-type material may be provided. Furthermore, by providing the field plate structure and the guard ring structure side by side, a higher dielectric breakdown suppression effect can be obtained. Note that these field plate structures and guard ring structures can also be applied to the gallium oxide diode 1 according to the first embodiment.

[0050] In the gallium oxide diode 2, by applying a forward voltage (positive potential on the anode electrode 22 side) between the anode electrode 22 and the cathode electrode 23, the potential barrier at the interface between the mesa-shaped portion 205 of the Ga2O3 layer 20 as viewed from the Ga2O3 layer 20 and the oxide semiconductor layer 21 is lowered, and a current flows from the anode electrode 22 to the cathode electrode 23.

[0051] On the other hand, when a reverse voltage (anode electrode 22 side has a negative potential) is applied between the anode electrode 22 and the cathode electrode 23, no current flows due to a potential barrier at the interface between the mesa-shaped portion 205 of the Ga2O3 layer 20 and the oxide semiconductor layer 21. Furthermore, when a reverse voltage is applied between the anode electrode 22 and the cathode electrode 23, a depletion layer spreads from the trench insulating film 24 side to the mesa-shaped portion 205 of the Ga2O3 layer 20, making it difficult for a current to flow in the reverse direction. Therefore, the gallium oxide diode 2 has a superior breakdown voltage due to the trench MOS structure.

[0052] The electric field strength in the gallium oxide diode 2 is hardly affected by the planar pattern of the trench 203. Therefore, regardless of the planar pattern of the trench 203, an excellent breakdown voltage can be obtained.

[0053] Third embodiment The third embodiment of the present invention is different from the first and second embodiments in that the gallium oxide diode has a trench-type junction barrier Schottky (JBS) structure. Note that the description of the same points as the first and second embodiments will be omitted or simplified.

[0054] (Configuration of Junction Barrier Schottky Diode) 4 is a vertical cross-sectional view of a gallium oxide diode 3 according to a third embodiment. The gallium oxide diode 3 is a vertical Schottky barrier diode having a trench type JBS structure.

[0055] The gallium oxide diode 3 comprises a substrate 301, an epitaxial layer 302 which is a layer formed on the substrate 301 and has a trench 303 opening on a surface 304 opposite the substrate 301 (the anode electrode 32 side), a p-type semiconductor member 34 embedded in the trench 303, an anode electrode 32 formed on the surface 304 side of the epitaxial layer 302, an oxide semiconductor layer 31 formed between the anode electrode 32 and a mesa-shaped portion 305 between adjacent trenches 303 of the epitaxial layer 302, and a cathode electrode 33 formed on the surface of the substrate 301 opposite the epitaxial layer 302.

[0056] The substrate 301 and the epitaxial layer 302 correspond to the substrate 101 and the epitaxial film 102 in the first embodiment, respectively, and constitute the Ga2O3 layer 30 corresponding to the Ga2O3 layer 10 in the first embodiment. The materials of the substrate 301 and the epitaxial layer 302 may be the same as those of the substrate 101 and the epitaxial film 102, respectively.

[0057] The oxide semiconductor layer 31 corresponds to the oxide semiconductor layer 11 according to the first embodiment. The material of the oxide semiconductor layer 31 may be the same as the material of the oxide semiconductor layer 11. The oxide semiconductor layer 31 has the same thickness as the oxide semiconductor layer 11. At least a part of the oxide semiconductor layer 31 is formed between the mesa-shaped portion 305 between the adjacent trenches 34 of the Ga2O3 layer 30 and the anode electrode 32. The oxide semiconductor layer 31 may be a single continuous film formed to cover the surface 304 of the epitaxial layer 302, as shown in FIG. 4.

[0058] The anode electrode 32 corresponds to the anode electrode 12 according to the first embodiment. The material of the anode electrode 32 may be the same as the material of the anode electrode 12.

[0059] The electron affinity of the oxide semiconductor layer 31 is larger than the electron affinity of the epitaxial layer 302, which is the portion of the Ga2O3 layer 30 that is in contact with the oxide semiconductor layer 31, and rectification is ensured by the offset of the conduction band minimum at the junction between the mesa-shaped portion 305 of the Ga2O3 layer 30 and the oxide semiconductor layer 31.

[0060] The difference Δχ between the electron affinity of the oxide semiconductor layer 31 and the electron affinity of the portion of the Ga2O3 layer 30 in contact with the oxide semiconductor layer 31 is preferably 0.4 eV or more, and more preferably 0.6 eV or more, similar to the difference Δχ between the electron affinity of the oxide semiconductor layer 11 and the electron affinity of the Ga2O3 layer 10 in contact with the oxide semiconductor layer 11.

[0061] The oxide semiconductor layer 31 is in contact with the mesa-shaped portion 305 of the Ga2O3 layer 30, but since it is an oxide, there is no risk of the reliability of the gallium oxide diode 2 being reduced by oxidation caused by oxygen contained in the Ga2O3 layer 30. The anode electrode 32 is in contact with the oxide semiconductor layer 31, but even if the anode electrode 32 is oxidized by oxygen contained in the oxide semiconductor layer 31, there is almost no effect on the ohmic junction between the anode electrode 32 and the oxide semiconductor layer 31, so there is almost no effect on the reliability of the gallium oxide diode 3. The cathode electrode 33 is in contact with the Ga2O3 layer 30, but even if the cathode electrode 33 is oxidized by oxygen contained in the Ga2O3 layer 30, there is almost no effect on the ohmic junction between the cathode electrode 33 and the Ga2O3 layer 30, so there is almost no effect on the reliability of the gallium oxide diode 3.

[0062] In addition, the gallium oxide diode 3 may have a field plate structure as shown in FIG. 4 in order to suppress dielectric breakdown at the electrode end and further improve the breakdown voltage. That is, an insulating film 35 may be provided around the anode electrode 32 on the surface 304 of the epitaxial layer 302, and the edge of the anode electrode 32 may ride on the insulating film 35. The material of the insulating film 35 may be the same as the material of the insulating film 25 according to the second embodiment. Also, instead of the field plate structure, a guard ring structure made of a p-type material may be provided. Also, by providing both the field plate structure and the guard ring structure, a higher dielectric breakdown suppression effect can be obtained.

[0063] In the gallium oxide diode 3, by applying a forward voltage (positive potential on the anode electrode 32 side) between the anode electrode 32 and the cathode electrode 33, the potential barrier at the interface between the mesa-shaped portion 305 of the Ga2O3 layer 30 as viewed from the Ga2O3 layer 30 and the oxide semiconductor layer 31 is lowered, and a current flows from the anode electrode 32 to the cathode electrode 33.

[0064] On the other hand, when a reverse voltage (anode electrode 32 side has a negative potential) is applied between the anode electrode 32 and the cathode electrode 33, no current flows due to a potential barrier at the interface between the mesa-shaped portion 305 of the Ga2O3 layer 30 and the oxide semiconductor layer 31. Furthermore, when a reverse voltage is applied between the anode electrode 32 and the cathode electrode 33, a depletion layer spreads from the p-type semiconductor member 34 side to the mesa-shaped portion 305 of the Ga2O3 layer 30, making it difficult for a current to flow in the reverse direction. Therefore, the gallium oxide diode 3 has a superior breakdown voltage due to the trench-type JBS structure.

[0065] The electric field strength in the gallium oxide diode 3 is hardly affected by the planar pattern of the trench 303 (planar pattern of the p-type semiconductor member 34). Therefore, regardless of the planar pattern of the trench 303, an excellent breakdown voltage can be obtained.

[0066] 4, the trench 303 is filled only with the p-type semiconductor material 34, but the oxide semiconductor layer 31 or the anode electrode 32 may partly extend into the trench 303. For example, the gallium oxide diode 3 may have a structure corresponding to the structure of the gallium oxide diode 2 in which the trench insulating film 24 is replaced with a p-type semiconductor material. That is, in the gallium oxide diode 3, it is sufficient that the inner surface of the trench 303 is covered with the p-type semiconductor material 34.

[0067] (Effects of the embodiment) According to the gallium oxide diodes 1, 2, and 3 according to the above-described embodiments of the present invention, rectification is ensured at the junctions between the Ga2O3 layers 10, 20, and 30 and the oxide semiconductor layers 11, 21, and 31, and oxidation of the anode electrodes 12, 22, and 32 does not affect the reliability of the gallium oxide diodes 1, 2, and 3. In other words, the gallium oxide diodes 1, 2, and 3 have a structure that can prevent a decrease in reliability due to oxidation of the electrodes.

[0068] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. Furthermore, the components of the above embodiment can be combined in any manner without departing from the spirit of the invention.

[0069] In addition, the above-described embodiments do not limit the scope of the invention according to the claims. Also, it should be noted that not all of the combinations of features described in the embodiments are essential to the means for solving the problems of the invention. [Explanation of symbols]

[0070] 1, 2, 3... gallium oxide diode; 10, 20, 30... Ga2O3 layer; 11, 21, 31... oxide semiconductor layer; 12, 22, 32... anode electrode; 13, 23, 33... cathode electrode; 24... trench insulating film; 203, 303... trench; 204, 304... surface; 205, 305... mesa-shaped portion; 34... p-type semiconductor member

Claims

1. n-type Ga ２ O ３ Layers, The Ga ２ O ３ an n-type oxide semiconductor layer stacked on the n-type oxide semiconductor layer; an anode electrode that forms an ohmic junction with the oxide semiconductor layer; The Ga ２ O ３ a cathode electrode forming an ohmic contact with the layer; Equipped with the oxide semiconductor layer has a donor concentration of 1×10 18 cm −3 or more; The electron affinity of the oxide semiconductor layer is ２ O ３ the electron affinity of the Ga ２ O ３ Rectification is ensured by an offset of the conduction band minimum at a junction between the oxide semiconductor layer and the oxide semiconductor layer. Gallium oxide diode.

2. The Ga ２ O ３ The electron affinity of the Ga of the oxide semiconductor layer ２ O ３ The difference in electron affinity between the layer and a portion in contact with the layer is 0.4 eV or more.

2. The gallium oxide diode of claim 1.

3. The oxide semiconductor layer is made of ZnO, TiO ２ , In ２ O ３ , SnO ２ The oxide semiconductor layer is made of an oxide semiconductor material including at least one of the following:

3. A gallium oxide diode according to claim 1 or 2.

4. The oxide semiconductor layer is made of a plurality of oxide semiconductors having different electron affinities. The gallium oxide diode according to any one of claims 1 to 3.

5. The oxide semiconductor layer has a thickness of 10 nm or more. The gallium oxide diode according to any one of claims 1 to 4.

6. The Ga ２ O ３ the layer has a trench on the surface facing the anode electrode, the inner surface of the trench is covered with a trench insulating film; a portion of the anode electrode is embedded inside the trench insulating film in the trench; At least a part of the oxide semiconductor layer is ２ O ３ a mesa-shaped portion between adjacent trenches of the layer and the anode electrode; The gallium oxide diode according to any one of claims 1 to 5.

7. The Ga ２ O ３ the layer has a trench on the surface facing the anode electrode, The inner surface of the trench is covered with a p-type semiconductor material, At least a part of the oxide semiconductor layer is ２ O ３ a mesa-shaped portion between adjacent trenches of the layer and the anode electrode; The gallium oxide diode according to any one of claims 1 to 5.

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